1. Technical Field
The present invention relates to methods and systems of preventing relay attacks of the type where signals are relayed from one device to another device in a manner that deceives a transmitting entity of the proximity of a device intended to receive the relayed signals.
2. Background
A relay attack is an attack on a wireless communication system where signals are relayed from one device to another device in a manner that deceives a transmitting entity of the proximity of a device intended to receive the relayed signals. A passive entry system (PES) used to facilitate access to a vehicle is one type of wireless communication system that is susceptible to a relay attack. The PES is configured to automatically allow vehicle entry, and in some cases, vehicle start as a long as a fob authorized by a PES controller within the vehicle is within a certain proximity.
Thieves have developed a system that initially relays the PES signals a greater distance away from the vehicle to an unsuspecting fob and then relays the fob's response back to the vehicle as if the fob was in close proximity. Since the fob is configured to respond to any messages received from the PES controller, even if the message was relayed to the fob with a relay attack system, the fob will respond in kind. In some cases, the fob may have a transmission range that allows its response to reach the vehicle without having to be relayed by the thieves. Thinking the fob must be within the required proximity in order to respond to the PES signals, the PES controller may unlock or start the vehicle upon receipt of the relayed response of the fob.
Some PES systems may include random numbers, high-level encryption, and rolling codes within the PES message in an effort to counteract the relay systems. These measures may make it a difficult for a relay system to relay message in correspondence with the vehicle PES controller rapidly changing the numbers and encryption requirements. These measures have been counteracted at least to some extent with newer relay attack systems having more sophisticated capabilities. Some PES system may included time of flight (TOF) and other temporal based scenarios to gauge time delays associated with the signaling relay employed by a relay attack system relaying the PES signals beyond the desired proximity to the vehicle. Such systems, however, can be problematic since they require acute temporal accuracy in order to properly measure TOF.